The present invention relates to an optical transmission module, and particularly to a receptacle-type optical transmission module having an optical transmitter module or an optical receiver module.
A receptacle-type optical transmission module is configured such that a coaxial can package or box-type package in which a light emitting element or a light receiving element is stored and sealed and a circuit substrate in which electronic components are implemented (a transmission control circuit of a peripheral circuit of the light emitting element or the light receiving element) are stored in one case. The receptacle-type optical transmission module also has a receptacle-type optical connector integrally formed with the case so as to connect an optical transmission plug to the coaxial can package or box-type package from the outside. The optical transmitter module or optical receiver module of the coaxial can package or box-type package is fixed to the case. Such a receptacle-type optical transmission module is described in Patent References 1 to 3. Here, Patent Reference 1 is the US counterpart of Patent References 2 and 3.
Patent References 4 and 5 describe an optical semiconductor module having a movable ferrule. Further, Patent References 6 to 9 describe an optical connector which is characterized in the configuration of a hook.
Incidentally, in the present specification, the optical transmitter module and the optical receiver module are collectively referred to as an optical communication module.
FIG. 1 is a partial cross-sectional view of an optical transmission module case storing an optical communication module. In FIG. 1, an optical communication module 300 is stored in an optical transmission module case 15 having a receptacle part 5 for connecting an optical transmission plug from the outside of the optical transmission module. The optical communication module 300 is provided inside with optical coupling surface 700 for optical coupling with a ferrule end of the optical transmission plug that is connected from the outside of the optical transmission module. In the case of a receptacle for an SC connector, the optical transmission module case 15 has a hook part 15a for holding the SC connector. An inner position of the hook part 15a is referred to as a mechanical reference surface. Further, the optical coupling surface through which light can be coupled and transmitted when the optical transmission plug and the optical communication module 300 are connected is referred to as an optical reference surface. The distance between the mechanical reference surface and the optical reference surface is 7.0±0.1 mm. This distance is referred to as E dimension. Although the optical transmission plug is not shown in FIG. 1 for ease of illustration, the real E dimension is the distance between the inner position of the hook and the optical coupling surface of the optical communication module when the optical transmission plug is inserted into the optical transmission module. This is common to the whole description in this specification.
FIG. 2 is a partial cross-sectional view of an optical transmission module case storing the optical communication module and a hook part. In FIG. 2, the optical communication module 300 is stored in an optical transmission module case 16, together with the receptacle part 5 for connecting the optical transmission plug from the outside of the optical transmission module and a hook part 30 for holding the optical transmission plug. The difference between the optical transmission module of FIG. 2 and the optical transmission module of FIG. 1 is that the hook part is separate from the optical transmission module case or integrally formed therewith. The dimensional relationship in FIG. 2 is the same as in FIG. 1.
FIG. 3 is a partial cross-sectional view of an optical transmission module case storing an optical communication module for LC connector. In FIG. 3, an LC connector-type optical communication module 350 is stored in an optical transmission module case 17 having a receptacle part 7 for connecting an optical transmission plug from the outside of the optical transmission module. The optical communication module 350 is provided inside with optical coupling surface 750 for optical coupling with a ferrule end of the optical transmission plug that is connected from the outside of the optical transmission module. The LC connector has a hook mechanism for holding the optical transmission plug. The held position of the hook mechanism is referred to as the mechanical reference surface. Further, the optical coupling surface through which light can be coupled and transmitted when the optical transmission plug and the optical communication module 350 are connected is referred to as the optical reference surface. The distance between the mechanical reference surface and the optical reference surface is 9.95±0.05 mm. This distance is referred to as B dimension.    [Patent Reference 1] U.S. Pat. No. 6,071,016.    [Patent Reference 2] Japanese Patent Application Publication No. Hei 10-247740.    [Patent Reference 3] Japanese Patent Application Publication No. Hei 10-247742.    [Patent Reference 4] Japanese Patent Application Publication No. Hei 10-246839.    [Patent Reference 5] Japanese Patent Application Publication No. Hei 11-337770.    [Patent Reference 6] Japanese Patent Application Publication No. 2005-309028.    [Patent Reference 7] Japanese Patent Application Publication No. Hei 10-170759.    [Patent Reference 8] Japanese Patent Application Publication No. Hei 10-160966.    [Patent Reference 9] Japanese Patent Application Publication No. HEI 10-170763.
The optical transmitter module or optical receiver module described in the above Patent References 1 to 3 is fixed to a case of the optical transmission module. Further, the optical transmission plug connected to the optical transmission module has an optical fiber at the back. In a device with the optical transmission module mounted thereon, a tensile force may be applied to the optical fiber in order to bundle many optical fibers. Because of the tensile force, stress is applied to the ferrule of the optical transmission plug, which is likely to prevent the light from being coupled or likely to cause damage of the optical transmitter module or optical receiver module.